1 Field of the Invention
The present invention relates generally to gravure printing and, more particularly to novel and highly effective apparatus for making a plate cylinder of an intaglio plate that can be used in gravure printing.
2. Description of the Prior Art
Various kinds of printing systems have been proposed, which effect relief printing, offset printing, intaglio printing, silk screen printing or the like. Intaglio printing is frequently used to print multiple copies of an image such as a photograph at high speed. A method of manufacturing a gravure printing plate, which is most practical in intaglio printing, will be explained with reference to FIGS. 1A to 1F.
The lights and shades of a document (e.g. a photograph) are developed on the surface of the plate cylinder for gravure printing in such a manner that holes are made whose areas or depths correspond to the lights and shades. Then the metal surface of the plate cylinder is etched to form collections of small cells or concave portions of different areas or of different depths, and an ink is filled into these concave portions, thereby carrying out the printing.
In the conventional method of manufacturing a gravure printing plate, a gelatin film 2 is coated on a paper 1 as shown in FIG. 1A to form a carbon tissue 3, and the carbon tissue 3 is immersed in an aqueous solution of potassium dichromate so as to give a photosensitive property thereto.
As shown in FIG. 1B, the carbon tissue 3 is then exposed to light through a mesh screen 4 having a mesh size of 8 lines/mm. The exposed carbon tissue 3 is subsequently exposed to light by using a positive film 5 wherein a picture to be printed is recorded. The gelatin film 2 is thereby hardened at its exposed portion.
Next, as shown in FIG. 1C, the gelatin film 2 of the carbon tissue 3 is deposited on a copper cylinder 6, and the paper 1 is removed.
The gelatin film 2 at its portions that have not been hardened by the exposing process is then dissolved in hot water (about 40.degree. C.) and removed, as shown in FIG. 1D.
The surface of the copper cylinder 6 is then etched by the immersion-diffusion process using an aqueous solution of ferrous chloride, as shown in FIG. 1E.
The hardened gelatin film 2 is removed to produce a gravure printing plate 7, as shown in FIG. 5F. This gravure printing plate 7 is used as a plate cylinder 7.
The plate cylinder 7 thus formed is partially immersed into a solvent-type ink 10 as shown in FIG. 2, and any excess ink 10 on the surface of the plate cylinder 7 is removed by a doctor blade 11. The doctor blade 11 is a knife having a sharp edge and is urged against the surface of the plate cylinder 7 so that the doctor blade 11 removes essentially all of the ink except that which is filled into a large number of concavities (these concavities will hereinafter be referred to as cells) formed on the printing surface of the plate cylinder 7.
An impression cylinder 12 presses a paper 13 to be printed against the printing surface of the plate cylinder 7, whereby the paper 13 adsorbs the ink 10 as shown in FIG. 3. The concentration of the ink 10 adsorbed is changed with the depths of the cells formed on the printing surface of the plate cylinder 7 by the etching process. In particular, a cell of relatively great volume (i.e. of relatively great area or depth) contains a relatively large amount of ink so that the concentration of the ink is relatively high, whereas a cell of relatively small volume (i.e. of relatively small area or depth) contains less ink so that the concentration of the ink is relatively low.
The plate cylinder for gravure printing according to the prior art is custom-manufactured for each printing process and is suitable for producing a large number of copies. However, if this plate cylinder is used for printing only several tens or several thousands of copies, the printing cost per copy is considerably increased. Further, the plate cylinder for the prior-art gravure printing requires not only a complicated manufacturing process but also a process for making a transparent positive image film, so that an increased number of process steps is required. Furthermore, it is necessary that copper be plated on the plate cylinder 7 and that a metal cylinder be employed for the etching process. Thus the manufacturing process for the plate cylinder is increased in scale and too expensive to be suitable for office use or personal use.